Storm monitor

ABSTRACT

A storm monitoring apparatus and method is described wherein two H-field antennas are oriented with respect to the heading axis of an aircraft or the like at an angle of 45°. The signals developed by these two antennas are picked-up by small R-F transformers which serve the inherent function of integrating the signals and extracting the H-field current component. A printed circuit board structuring of the two antennas provides for consistency of fabrication and reliability as well as compactness. The monitoring apparatus exhibits broad band frequency response to evaluate lightning strike rate to determine storm range and intensity. A computer control test utilizing diagnostic coils at the antenna carries out periodic testing of the performance of the device and a component such as a gravity switch provides an indication to the control system as to the orientation of mounting of the antenna on an aircraft. The outputs of the antennas are digitized and evaluated at a high rate and range information is developed from these digitized data in consequence the transfer function of the atmosphere. For example, range is developed by an analysis of the decay of various frequency components emanating from a lightning burst. Select memory retention of the data is continuously provided such that the operator can look to immediately preceding storm evaluations to determine whether the condition in which flight is being made is one into worsening or improving weather.

BACKGROUND OF THE INVENTION

The aircraft industry has long been concerned with the development ofsafe flight procedures in the presence of inclement weather. Aircraftweather monitoring instrumentation involves a variety of devicesincluding radar-and ground-derived weather information readouts, as wellas instruments performing in specific response to thunderstormphenomena. These latter monitoring instruments are desirable inasmuchas, although radar maps rain with great accuracy, rain is not thepilot's main concern. Hazardous convective activity occurs long beforeany rain has fallen. Thus, it is helpful to identify thunderstorms whereradar indicates nothing.

Thunderstorms have long been studied and evaluated by investigators.Some categorizations of them have been advanced as part of an analysisleading to the detection and mapping instrumentation. For example, inU.S. Pat. No. 4,023,408 by Ryan, et al., issued May 17, 1977, andentitled "Stormscope", thunderstorms are classified into two basictypes, the convective thunderstorm and the frontal thunderstorm. Thediscourse provided therein describes the development through maturity ofeach type storm. In general, the storms exhibit very fast dischargephenomena which, when monitored, provides an extensive amount of datadeveloped from strikes of a duration on the order of 100 microseconds.Thus, to fully evaluate the storms, it is important that a broad-bandresponse be made to them. Generally, a storm-generated lightning boltwill be present as an extremely large current surge from cloud toground. Accompanying that surge of current is a magnetic field whichpropagates as any radiowave for many, many hundreds of miles. With eachsuch electromagnetic wave, there are two components, a magneticcomponent or H-field, and an electrostatic component or E-field. TheE-field is nondirectional as far as antenna evaluation thereof isconcerned and thus, its influence on any antenna structure serves tocontaminate directional information. Typically, the instrumentsheretofore developed employ a technology wherein three antennas areutilized, two being H-field antennas and a third being an E-fieldantenna. The latter E-field antenna has represented an unfortunate majorsource of noise and confusion to the circuitry of these storm monitors,inasmuch as it responds quite well to noise phenomena and thus is quiteunreliable. This latter third antenna is used to resolve ambiguity whichresults from recourse by instruments of the past to low bandwidthperformance. The use of this third antenna results, more than likely,because of its use typically in automatic direction finding devices.Such devices have typically employed a pair of cross coils and a thirdE-field antenna to resolve ambiguities. However, in the automaticdirection finding environment, the signal monitored is continuous,whereas when this system is employed in ranging and locatingthunderstorms, the signal relied upon is that emanating from thelightning strike, and thus is a mere random pulse of generally knownpolarity. Thus, the third, E-field antenna conventionally employed withthe thunderstorm evaluating and monitoring instrumentation hasrepresented a problematic aspect of those devices.

Conventional storm monitoring instruments have employed two orthogonallydisposed H-field coils which are formed as wire windings about a ferritecore. Such wound structures may pose difficulties in costs in assembly.This core-and-coil assemblage is then mounted within an antenna pod onthe aircraft such that one coil is oriented perpendicularly with respectto the longitudinal or flight-heading axis of the aircraft. Stormbearing information thus is developed in conjunction with aircraftbearing or heading. However, the perpendicular orientation of one of theH-field antennas with respect to heading results in storm-bearingresponse characteristics which are the least accurate for the aircraftheading direction. Further, the attitude of the aircraft typicallyevokes a vertical movement or pivoting of the antenna coils duringconventional flight. This results in signal anomalies. Another aspect ofthis conventional H-field antenna implementation concerns its output,which is a function of the derivative of the magnetic field. Thus,integration approaches are employed which are undesirable in suchmeasurement systems.

The aircraft environment also poses problems for storm monitoringinstrumentation. Thus, testing of such equipment before flight or theinstallation of the equipment generally cannot evaluate the effects ofthe dynamic and noisy environment of an aircraft in flight. During suchflight, cabling carrying antenna-derived signals will be subjected tothe noise influence of aircraft heater motors, strobe light powersupplies, autopilot motors and the like. This, of course, represents ahighly noisy and rigorous environment to derogate the value of thesignals transmitted. Installation anomalies also may occur. The antennamay be installed backwards or upside down by unskilled technicians ormechanics. Wiring to the H-field antennas may be reversed to generatejust the opposite of information desired. Finally, the readoutcomponents should be of practical size and weight for instrument panelmounting. Typically, relatively long cathode ray tube (CRT)-basedreadout devices are employed, requiring specialized mounting due totheir inherently larger bulk.

SUMMARY

The present invention is addressed to a storm monitoring apparatus andmethod employing two H-field antennas which are orthogonally disposedwith respect to each other, but additionally are each oriented at anangle of 45° to the line-of-flight or heading-axis of the aircraft. Thisorientation achieves enhanced signal-to-noise performance and higheraccuracy for locating storms, especially those storms positionedstraight ahead of the aircraft. Further, the antennae, so oriented withrespect to the aircraft line of flight, exhibit an immunity to aircraftattitude variations with respect to output signal generation and areemployed in a manner to achieve a common mode rejection of otherwisecontaminating E-field signals. This common mode rejection is developedthrough the employment of current-specific detectors, such as small, R-Foutput transformers performing in conjunction with the H-field antennas.A rejection ratio on the order of 500:1 or 600:1 is achieved with theunique approach. Of additional merit, the output signals of the antennasare directly proportional to the H-field transient produced by alightning strike due to an inherent integration achieved with detectorinductance and impedance. Thus, no integration-based anomalies due to aspecific integration stage are encountered with the instrumentation.

Formed utilizing printed circuit procedures encasing or enclosing aferrite core, the antennas exhibit a consistency of performance andquality over devices produced employing coil winding procedures.

The antennas are enclosed within a low profile, aerodynamicallyelliptically-shaped housing formed of high-strength plastic materialwithin which conductive material is incorporated to minimize electricfield pick-up. Formed as part of a readily-reproducible circuit boardassemblage incorporating a ground plane for improved avoidance ofE-field contaminants, the antennas are fabricated with desirableconsistency, thus promoting reliable performance. As part of thiscircuit board structuring, a ferrite block, representing highest mass ofthe sensor structure, is restrained upon and within the circuit boardarrangement in a manner securing the assemblage from damage due to thesubstantial vibration encountered during flight. A gravity switch withinthe antenna housing provides an output to the control system indicatingthe orientation of the antennas. Thus, should a mechanic mount thehousing in a manner considered upside down, the gravity switch willaccommodate for that error with appropriate signals to the on-boardcontrol system.

The control system employed with the apparatus performs in conjunctionwith test coils and test coil drivers mounted adjacent the H-fieldantennas. By carrying out automatic and periodic diagnostic testing ofthe antennas and associated response circuitry during inflight usage,the pilot has an assurance of reliability of performance on asubstantially continuous basis. Reliability is additionally enhancedthrough the utilization of a built-in power supply regulator within theantenna housing, functioning to minimize interaction between the antennaand electrical equipment sharing the aircraft power supply.

The readout providing storm bearing and range location to the pilot ispositioned within the aircraft cabin, a square pixel matrix, neon plasmadisplay device being employed. In addition to exhibiting substantiallyreduced bulk, the matrix-based display is rotated 45° with respect tovertical to achieve an improved clarity of storm map presentation forthe operator or pilot. A circularly-polarized optical filter is placedin front of this display to minimize the effects of glare. Edgeillumination is provided with the display such that markings are visibleunder low ambient light levels, and, these levels are monitored so as tooptimally adjust indicia illumination. Included with the readout arepush-button switching actuators which provide for gain changing througha smooth, continuous "zooming" action. Additionally, historical stormcell map data are stored in memory and may be "replayed" on a"time-lapse" basis for the operator. In the event of the automaticselftesting or self-diagnostics showing an error, an appropriate errormessage is published at the display.

The control system employed with the invention treats the signalsderiving, inter alia, from the H-field antennas by digitizing them todevelop a string of binary numbers which are stored at very high speedin memory. The thus-digitized data are examined in real time by athreshold form of circuit to determine whether the system has interestin the data as being evolved from a thunderstorm. The system thendetermines the strength and height of the storm based upon the strikerate examined, while range is developed in consequence of the transferfunction of the atmosphere. In this regard, the frequencies developed bythe broad-band system will decay within the atmosphere at differentrates depending upon frequency value. By analyzing these rates of decay,range can be evolved with a high level of precision.

Other objects of the invention will, in part, be obvious and will, inpart, appear hereinafter.

The invention, accordingly, comprises the apparatus, system and methodpossessing the construction, combination of elements, arrangement ofparts and steps which are exemplified in the following description.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial perspective view of the antenna housing employedwith the invention shown attached to a vehicle with which it performs,such as the underside of an aircraft.

FIG. 2 is a schematic block diagram showing the components incorporatedwithin the antenna housing of FIG. 1.

FIG. 3 is an exploded view showing the principal components of theantenna assemblage of FIG. 1.

FIG. 4 is an exploded view of the circuit board structure componentshown assembled in FIG. 2.

FIG. 5 is a top view of the base component of a circuit board employedwith the structure shown in FIGS. 2 and 3.

FIG. 6 is a partial view of a retainer and coil-supporting circuit boardshown in FIGS. 2 and 3.

FIG. 7 is a view of the circuit board assemblage of FIG. 5 showing indotted line fashion the coil structuring of its underside.

FIG. 8 is a block diagrammatic representation of the cabin-mountedinstrumentation employed with the sensor assembly shown in FIG. 1.

FIG. 9 is a front view of a display readout mounted within the cabin ofan aircraft.

FIG. 10 is a schematic diagram of a display driver circuit having anoverlay of the lens with markings shown in FIG. 9 positioned thereon.

FIG. 11 is an electrical schematic diagram of the block diagram shown inFIG. 2.

FIG. 12 is a block diagram of the relationship of control tasks with ascheduler program.

FIG. 13 is a flow chart showing the activities of a background signaltest generator.

FIG. 14 is a flow diagram showing a data-acquisition control interruptactivity.

FIG. 15 is a flow chart showing a background signal processing activity.

FIG. 16 is a block diagram showing the activities associated with asynchro-heading input to a control system.

FIG. 17 is a flow diagram of a display controller interrupt-basedactivity.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, an antenna or sensor assemblage configured inaccordance with the invention is revealed generally at 10. Antennaassemblage 10 includes an outer housing 12 having a cover 14 formedthereon. The housing and cover are formed of a highly impact resistantplastic material, such as nylon, which is made conductive by beingimpregnated, for example, with a carbon component. The device 10 ismounted, for example, on the underside of an aircraft, a portion ofwhich is represented at 16. To align the antenna appropriately, asilhouette 18 of an aircraft is formed upon the lid component 14. Thisis to aid the aircraft technician in aligning the antenna within thehousing 12 with the longitudinal axis of the vehicle 16, i.e., theheading axis 20. A gravitational switch also included within the device12 provides an output signal indicative as to whether the housing 12 ismounted on the lower side of an aircraft or on the upper side. Thispermits the microprocessor-driven control system to accommodate for suchmounting, and thus avoid the occurrence of any error on the part of thetechnician in mounting the system within an aircraft.

Looking to FIG. 2, a schematic representation of the components whichare within the sensor assemblage 10 are revealed. In the figure, theheading axis 20 again is reproduced and is seen to diagonally extendacross a square ferrite block 22 which functions in the conventionalmanner as an enhancement for antenna response to the electromagneticradiation emanating from a lightning strike. Represented adjacentferrite block 22 is a first H-field antenna coil 24 and, orthogonallydisposed with respect to the coil 24, is a second H-field antenna coil26. Note that coils 24 and 26 are represented in the figure as beingoriented with respect to the heading axis 20 at an angle of 45°. Where,for example, a lightning strike is directly ahead of the sensor 10, i.e.along the axis 20, the two coils 24 and 26 thus will be at an angle of45° to the origin of this signal. The signal received by both coils 24and 26 then is identical in amplitude. Alternately, if the axis 20 thenturns by 45°, the signal in one coil will drop to a zero amplitude whilethe other will become a maximum. This is a somewhat-conventional "FIG.8" form of response characteristics. However, the 45° orientation nowprovided with respect to axis 20 gives the most accurate bearinginformation. This literally holds true for the most important bearing athand in an aircraft operational situation, i.e. a storm which isdirectly before the aircraft. By contrast, the accuracy of bearinginformation is the least accurate where one of the coils is at 90° tothe point of origin of a lightning strike. The magnetic or H-fieldcomponent of an electromagnetic wave will be manifested in the windingsof antennas 24 and 26 as a current, while the electrostatic component orE-field component will not. Because the E-field its non-directional asit pertains to its reaction upon an antenna, is effect upon the windings24 and 26 may be considered an contamination of directional information.Thus, the pick-off or detection of the H-field magnetic component, whichis manifested as a current, is one which is, under the criteria of theinstant invention, selective to that current component. In effect, theE-field component becomes a common mode component, thus, by utilizing acurrent specific pick-off, a common mode rejection is achieved. This isdeveloped through the utilization of a small R-F current-detectingtransformer 28 in conjunction with antenna coil 24 and a correspondingsmall R-F current-detecting transformer 30 in conjunction with antennacoil or winding 26. A common mode or E-field rejection is thus achieved.Other current specific pick-offs may be employed, such as anopto-isolator having a light-deriving component, the intensity of whichis proportional to coil-generated current. However, the best modecontemplated for this current specific pick-off is the transformerarrangement as shown.

Because the signal generated at pick-offs 28 and 30 is of somewhat lowlevel, a preamplification thereof is carried out at preamplificationstage 32, having an amplified output represented at line 34. In similarfashion, the output of pick-off transformer 30 is preamplified atpreamplification stage 36 and the resultant output is provided asrepresented at line 38. The preamplification of the detected H-fieldsignals at the sensor 10 itself permits the transmission of signals tothe control circuitry within the aircraft cabin at a higher level and,thus, with more immunity to the noise and similar phenomena encounteredin aircraft flight. The 45° orientation of coils 24 and 26 also will beseen to render them substantially immune from attitude variations whichare common in aircraft flight. Thus, as the aircraft fuselage pivotsabout an axis transverse to the heading axis 20, the effect upon theresponse of windings 24 and 26 is far less than that, for example,exhibited by antenna windings which are oriented perpendicularly to theheading axis 20.

Of particular value to the performance of the system at hand, themicroprocessor-driven control carries out a periodic testing of theentire system by imposing antenna test signals into the antennastructure and evaluating the resultant diagnostic signals. This is shownin the figure as a first test coil 40 associated with winding 24 and asecond test coil 42 associated with antenna winding 26. These test coils40 and 42 are driven by test coil drivers represented at block 44. Asingle line 46 is shown feeding the test coil drivers 44. Only asingular line is used for this purpose to avoid error. The selection bythe control circuitry of which coil 40 or 42 to cause to be excited iselected through the corresponding election of the polarity of the signalimposed at line 46. Thus, one polarity input from line 46 will cause theexcitation of coil 40 for diagnostic purposes, while the application ofa test signal of opposite polarity from line 46 will cause theexcitation of coil 42 for diagnostic purposes. With the test arrangementshown, the pilot is afforded essentially a continuous assurance of theoperability of the system which, when needed, is of substantialimportance to an aircraft occupant.

Additionally incorporated within the sensor assembly 10 is a voltageregulator represented at block 50 having a power input represented atline 52. The gravity sensor discussed above may be provided as, forexample, a mercury switch. This gravity sensor is represented at block54 and is seen to provide an output at line 56. The gravity sensorprovides the control system with an indication as to the orientation ofthe antenna assemblage 10 such that appropriate accommodation may bemade in the development of bearing information. Finally, a polaritysensor may be provided with the sensor assemblage 10. This generatesinformation as to the polarity of the received electromagneticradiation. Such function may be implemented as a planar conductor withinthe sensor assembly 10 and is represented at block 58.

Turning to FIG. 3, the sensor assemblage 10 is represented in explodedfashion prior to its final assembly. In this regard, the quite compactand rigid eliptical housing 12 is shown formed having a cavity 70therein within which a printed circuit board assembly 72 is positioned.Upon the securement and appropriate potting of the assemblage 72 withinthe cavity 70, the lid 14 is attached using, inter alia, screwsrepresented at 74 in FIG. 1. Seen on this assemblage 72 is a firstprinted circuit board or substrate 76 which is located in spaced,mutually parallel adjacency with a second printed circuit board orsubstrate 78. The smaller printed circuit board 76 and the correspondingadjacent portion of circuit board 78 will be seen to carry printedconductive coil lines or stripes for forming the H-field coils 24 and26. The printed substantially-parallel line arrays representing thesecoil windings are interconnected from one substrate 76 to the other 78by arrays of peripherally disposed conductive pins, representedgenerally at 80. Within these arrays of pins, which extend about thesquare peripheries of the coil defining circuit boards 76 and 78 is asquare ferrite block 82. Looking additionally to FIG. 4, an explodedrepresentation of the assembly of ferrite block 82, circuit boards 78and 76 and pin arrays 80 is revealed. The ferrite block 82 is retainedrigidly in position and in intimate association with the printed circuitboards 76 and 78 both by adhesive attachment and through the utilizationof plastic retainers 84 through which the individual pins of the array80 extend and are supported. The pins of the array 80 function tocomplete the formation of coils 24 and 26. This is achieved by anassociation of parallel line arrays for one coil located at the first ortop surface 86 of substrate 76 and the top surface 88 of substrate 78.The printed circuit lines or stripes on the surfaces 86 and 88 then areconnected by corresponding pins of the array 80. These parallel lines asdefined at surfaces 86 and 88 are arranged in one 45° sense with respectto axis 20. The other H-field coil is formed at the bottom or secondsurface 90 of substrate 76 and at the corresponding bottom surface 92 ofsubstrate 78. As before, the space parallel line arrays areinterconnected to define coils by appropriate pin arrays 80. The linearrays at surfaces 90 and 92 are orthogonally disposed with respect tothe coil defining line arrays of surfaces 86 and 88. Thus, the alignmentof each antenna is at 45° with respect to axis 20. The small R-Fpick-off or detector transformers 28 and 30 are retained within brasshousings in close adjacency with the appropriate pins of array 80 in theassemblage. One such transformer assemblage is represented in FIGS. 3and 4 at 96. Additionally shown in these figures is the noted gravityswitch or sensor 54 and a cable output/input connector 100.

Turning to FIG. 5, the substrate or printed circuit board 78 isrevealed, additionally showing the top surface 88 thereof. Printed onthis surface 88 is the array 102 of printed conductive lines formingessentially one-half of one of the coils, for example, coil 24. Theoppositely-disposed line array of this coil 24 is shown in FIG. 6 as aline array 104 located on the top surface 86 of substrate 76. Theearlier-described pins within array 80 associated with the line arrays104 and 102 extend through the linear hole arrays 106 and 108 insubstrate 76 as shown in FIG. 6 downwardly vertically into correspondingrespective linear hole arrays 110 and 112 extending through substrate orprinted circuit board 78. Note that the lines of array 102 are at a 45°angle with respect to heading axis 20 again represented in FIG. 5 and,are parallel with the lines of array 104. The detecting transformer 28or, for example, that represented within the protective brass container96, is positioned at the outline 96' shown in FIG. 5. Note that thetransformer, as earlier represented at 28 in FIG. 2, is located inadjacency with the pins extending from hole array 106 through hole array110.

The bottom surface of circuit board or substrate 76 is represented againat 90 in conjunction with FIG. 7. This bottom surface 90 contains anarray of printed conductive lines represented generally at 114 and shownin phantom such that the angular relationship of these lines of thearray 114 may be observed to be in an orthogonal or perpendicularassociation with the corresponding array 104 at the top of substrate 76.A corresponding parallel array of printed conductive lines (not shown)is located on the bottom of the circuit board or substrate 78 as seen inFIG. 5 immediately below the line array 102. Note that the lines ofarray 114 extend between linear arrays of holes 118 and 120 whichreceive pins from the array 80 extending therefrom to corresponding holearrays within substrate 78 as shown in FIG. 5 respectively at 122 and124. An outline 98' is shown in FIG. 5 which is intended to receive thecurrent responsive transformer as at 30 such that it is in closephysical association with the coil components represented by the pinsextending through hole array 122.

The earlier-described test windings 40 and 42 (FIG. 2) are developedwith the printed circuit approach as windings formed of printedconductive lines and associated pins. In this regard, it may be observedin FIG. 6 that one such test winding printed line is shown at 125 and inFIG. 5 at 126. Correspondingly, a test winding 127 is provided withrespect to the bottom of substrate 76 which performs in conjunction witha corresponding conductive line (not shown) printed upon the bottom ofsubstrate 78.

Now considering the control system of the thunderstorm monitor, a cablecarries the data from sensor 10 via connection with earlier-describedconnector 100 to the control components located within the aircraftcabin. This control system treats the signals by digitizing them todevelop a string of binary numbers which are stored at very high speedin memory. For example, the system will typically carry out 20,000,000to 24,000,000 measurements per second. These data, as thus digitized,are examined in real time by a threshold responsive form of circuit todetermine whether the system has interest in the data as emanating froma thunderstorm. This evaluation is made on a digital basis. For example,when a key threshold is crossed, the instrument takes an additional 500samples and presents them to memory. An analysis is made of thedigitized signals and a number of key decisions are made as to whetherthe data emanated from a thunderstorm. This is based on thecharacteristics of thunderstorm signals. A determination then is made asto the bearing of the thunderstorm and measurements are evolved basedupon the strike rate of the thunderstorm to classify its strength andheight. The strike rate is represented as the number of strikes persecond and is a measure of the size of the thunderstorm, particularlyits height. In effect, by having a very accurate bearing and knowing therate at which strikes are coming in on this bearing, the system canidentify how strong the storm is, i.e. how tall and the like. Receivedsignal strength may be employed as an indication of strength. Thus,strike rate, heretofore considered only as an average, is specificallyemployed with the control system as a key required to classify stormintensity. The control system further carries out a Fourier transform onthe received data. This is because the transfer function of theatmosphere, i.e. the efficiency at which the atmosphere transmitsvarious frequencies varies with respect to the value of thosefrequencies. Certain of the frequencies are conducted through theatmosphere efficiently and some less efficiently, i.e. some decay at amore rapid rate than others. Inasmuch as it is known that thethunderstorm or strike produces a uniform amount of these frequencycomponents at the source, the ratio of components provides a highlyaccurate identification of range. Thus, the spectral distribution of theelectromagnetic radiation emanating from a strike is quite importantand, it is imperative that the instant system perform on a broad bandbasis in order to acquire all of the necessary data. In particular, thesensor or antenna assemblage 10 exhibits a very broad band, its responsecharacteristics being flat, for example from 50 KHz to 5 MHz. Incomparison with conventional storm monitoring devices, the instantsystem will make 2,000 measurements over the broad band of frequenciesnoted, while such conventional device will make one measurement within arestricted bandwidth.

Referring to FIG. 8, a block diagrammatic representation of the controlsystem is represented generally at 130. In the control, a microprocessorwith associated program (ROM) memory is provided as represented at block132. From this control 132, as represented by lines 134 and 136, dataare acquired through a multiplex amplifier function represented atblocks 138 and 140. In this regard, multiplexer function 138 isconsidered an "X" function as associated, for example, with H-field coil24. The multiplexer, accordingly, receives preamplified analog signalsfrom earlier-described line 34 (FIG. 2). Additionally, the multiplexingfunction 138 will select a corresponding heading X-synchro input asrepresented at line 142 from the aircraft navigational system. Further,a gain select function may be carried out in response to multiplexedselection and the control system may measure and accommodate for offsetby providing an offset output command via multiplexer 138 as representedat line 146. Multiplex amplifier function 140 is associated with a "Y"designated antenna corresponding, for example, with H-field antenna 26.This input again is represented at line 38 being selectable bymultiplexing function 140. Additionally, the multiplexer 140 may selectpolarity information via line 64; Y-synch inputs via line 148, and aphotocell input measuring cabin ambient lighting intensity via line 150.

The X-antenna input at line 34, when selected by multiplexing function138 is transmitted as represented by line 152 to an analog-to-digitalconverter function for this X-channel as represented at block 154. Insimilar fashion, the Y-antenna input data are, when selected,transmitted as represented at line 156 to an analog-to-digital converterstage represented at block 158. The 8-bit binary number stringsdeveloped from converters 154 and 158 then are delivered via databus 160to a digital signal processing function (DSP) represented as includingan acquisition trigger at block 170. The acquisition trigger 170 iscontrolled by an acquisition control function represented at block 172and line 174. The control 172, in turn, is controlled from themicroprocessor function 132 as represented by line 176. Acquisitiontrigger 170 carries out the noted threshold evaluation of incomingantenna-derived and digitized data and that which is selected issubmitted to acquisition memory as represented at block 178 via bus 180.Placement of data within memory 178 is under the address control of theacquisition control function 172 as represented by address bus 182. Themicroprocessor or control function 132 acquires the data so stored atmemory 178 by appropriate address commands via bus 184, the data flowfrom memory 178 to the microprocessor function 132 being represented atbus 186.

Additionally, non-multiplexed inputs and the like submitted to ortransmitted from the microprocessor function 132 will include theantenna test output as earlier described at line 146 and hereinrepresented by that numeration, as well as the gravity sensor input asearlier-described at line 56 and again shown with that line numeration.Further, a heading step input from the stepper function of an onboardcompass is submitted as represented at lines 188 and 190. Additionally,a serial data interface is made available as represented at line 192 anda lamp intensity control output is provided as represented at line 194.

Microprocessor function 132 performs in conjunction with a data memoryrepresented at block 200 which is addressed from the microprocessor asrepresented at bus 202 and bi-directional data exchange is providedbetween function 132 and memory 200 as represented by bus 204. Criticaldata also may be stored in non-volatile memory represented at block 206and communication with the microprocessor is provided via abidirectional one-line bus 208. The appropriate performance of themicroprocessor function 132 is monitored by a watchdog circuitrepresented at block 210 and line 212.

User function controls, particularly including hand actuable switches atthe display of the system, are represented at block 214 and theiractuation commands are submitted to microprocessor function 132 asrepresented by line 216. Following the processing of data on the part ofthe microprocessor function 132, that data then are submitted to displaymemory 218 via databus 220. The display memory address input from themicroprocessor function 132 with respect to submitted data is providedvia address bus 222. Data within memory 218 is submittable via databus224 to a display control represented at block 226. Display control 226,in turn, addresses the display memory 218 for selection of data asrepresented by address bus 228. The accessed data then may be submittedas represented at bus 230 to a plasma display and associated displaydrivers represented at block 232. Through the use of a plasma form ofdisplay, the large bulk otherwise associated with such displaycomponents as cathode ray tubes and the like is avoided.

The display function represented at block 232 in FIG. 8 is principallycomprised of a neon plasma display which ideally fits within a standardaircraft instrumentation hole. These holes are circular having adiameter of 31/8 inch. Looking to FIG. 9, the readout component of thedisplay is represented at 240 as including a housing component 242 whichis formed forwardy to define a circular bezel 244 which mounts throughthe noted instrument hole. The entire readout structure includingdisplay drivers has a widthwise or depth extent of about 1 inch and theprincipal component thereof is a 64×64 pixel matrix neon plasma display.Over the display is a plexiglass lens represented generally at 246 whichcarries indicia or legends intended to be lighted at night. Acircularly-polarized filter is also positioned before the plasma displayto provide an increase in contrast. For night illumination, one or moresmall lamps within the housing may provide edge lighting to illuminatethe legends positioned upon the plexiglass lens. Additionally, aphotocell may be employed for the purpose of monitoring the level ofcabin light to adjust the intensity of such illumination under thecontrol of the microprocessor 132, for example, as discussed inconnection with line 194 in FIG. 8. The legends at the display 232 onthe lens thereof, include a small airplane silhouette 248, the directionof which represents heading. Bearing marks 250 are provided as well asrange marks or circles 252 and 254. Shown in exaggerated scale at thedisplay 240 are storm indicators which are perceived by the aircraftpilot to be represented as groupings of diamond-shaped pixels as seen at256. These plasma-illuminated small square outputs identify thunderstormlocations with respect to the ranges represented by markers 252 and 254.In this regard, the outside range ring or marker 254 may represent 25,50, 100, or 200 miles. Correspondingly, the inside ring or marker 252will represent one-half of the range of the outside marker 254. SwitchS4 represents a clear button and switch S1 provides a "time travel"function. Actuation of switch S1 triggers a time-lapsed rendition ofrecent electrical activity. Up to 4,000 strikes are replayed at thedisplay in a matter of seconds to reveal important weather trends. Thisshows whether the aircraft is approaching a worsening weather conditionor an improving weather condition. A desirable aspect of the notedranging achieved with the actuation of switches S2 and S3 is in the"zoom" transition from one range to another. Rather than an abruptswitching from one range condition to the next, a smooth transitionoccurs to give the pilot further guidance as to the condition at hand.

Referring to FIG. 10, a schematic diagram of the plasma display andassociated driver components is provided in a manner wherein the lens246 and legends are superimposed thereon. This orientation shows the 45°relationship between bearing markings 250 and the 64×64 column/roworientation of the components of the display. This column/roworientation is represented generally at 260. The plasma output device isrepresented at 262 in conjunction with two anode drivers 264 and 266 aswell as two cathode drivers 267 and 268. Note in this regard that theoutput of anode driver 264 is provided at a 32 lead array 270 whichextends through an array of resistors represented at block 272 to anodecoupling with device 262. Similarly, anode driver 266 provides a 32 leadarray 274 which extends through a resistor array represented by block276 to device 262. Cathode driver 267 similarly has an output lead array278 which extends through a corresponding array of resistors representedby block 280 for connection with the cathode components of device 262.Cathode driver 268 similarly has an output at 32-lead array 282 whichextends through a corresponding array of resistors as shown at block 284for connection with device 262. The display 262 is addressed as a 64×64X-Y matrix wherein 64 anodes are driven in parallel and one cathode isenabled at a time. Both of the anode driver circuits and the cathodedriver circuits have serial data paths, the serial "out" terminal of onebeing coupled with the serial "in" terminal of the next. In this regard,serial data comes into the anode driver 266 from anode data line 286 asa sequence of 64 bits. Once the 64 bits are in place, a latch signal isprovided to fix the anode data within the driver chips. Upon beingfixed, a new string of 64 bits is initiated essentially immediately. Inthe cathode system, only a single output or bit is on in either drivercircuit 267 or 268 at a given time. Thus, a single bit is clockedthrough the system as emanating, for example, from line 288. A +80 vsupply is provided at line 290, while +12 v supply is provided at line292. Below the latter line, are three lines 294, 296, and 298 providing,respectively, an anode strobe, anode clock, and an anode enable input.Next, a lamp energization line is provided at line 300 for use inconjunction with lamps 301 serving to illuminate the lens. A lamp groundis provided at line 302. An array of lines then extend to switches S1-S4as described in connection with FIG. 9, the final line 305 being acommon. A photocell output extending from photocell 307 is provided atline 306, the signal ground being provided at line 308. A scaling andfiltering capacitor-resistor may be provided, as represented generallyat 309, for employment with the photocell 307. Photocell 307 monitorsthe intensity of cabin light and adjusts light intensity or brightnessof pixels within the display. The inputs then include a cathode enableinput at line 310, a cathode clock signal at line 312, -88 v supply atline 314 and -100 v supply at line 316.

Referring to FIG. 11, a schematic representation of the circuitryencapsulated within the sensor 10 is revealed at an enhanced level ofdetail. The components within this figure have been described inconjunction with FIG. 2. Accordingly, where appropriate, commonnumeration is retained. In the figure, the ferrite core 22 isrepresented by a core symbol in conjunction with the H-field antennawindings 24 and 26. While the symbolism of the windings is shown as adual winding arrangement, they remain a single winding as abovediscussed. Winding 24 is seen coupled by lines 330 and 332 to coaxialdistributed inductance/capacitance filters shown respectively at FL1 andFL2. These filters are formed of a ferrite material with a capacitancecoating about the outside thereof. Resistors R1 and R2 extending betweenlines 330 and 332 provide load impedance for the coil and the lines 330and 332 then extend to the primary of common mode rejection transformer28. Transformer 28 also supplies a modicum of gain, for example about5:1 through a step-up arrangement of its windings. It may be noted thatthe inductance of coil or windings 24 and the impedance provided byresistors R1 and R2 develop an inherent integration of the signalderived at winding 24. Thus, there is developed a straight measure ofstrike current without the necessity of interposing an integrationstage. In effect, magnetic flux is measured directly. The secondarywinding of transformer 28 is coupled with line 334 and ground line 336.Extending between these lines is a capacitor C1 and cross-coupled diodesD1 and D2. The latter components are present for transient protection.Line 344 is seen to extend to the positive input of an operationalamplifier 338 of preliminary amplification stage 32. High gain amplifier32 has a gain arrangement enhancing higher frequency. In this regard,the d.c. gain is determined by the combination of resistor R4 and theseries combination of resistors R3 and R5. As the frequency elevates,capacitor C2 serves to override or "swamp" resistor R5 causing the a.c.gain of the stage to increase. Thus, the d.c. offset is amplified withvery little gain and the a.c. signals are substantially amplified. Theoutput of amplifier 338 at line 342 extends through capacitor C3functioning to block a d.c. term to the primary winding of a couplingtransformer 340. A shielded, twisted line pair is utilized to direct theoutput from the preamplification stage to the instrumentation within theaircraft cabin. Any noise imposed on that shielded, twisted pair will bean E-field signal which otherwise would cause fluctuation at the output.However, inasmuch as these phenomena perform together and by virtue ofthe presence of transformer 340, an effective cancellation of suchphenomena occurs. The secondary of transformer 340 provides an output atlines 344 and 346 which is filtered by filters FL3 and FL4 which areidentical to corresponding filters FL1 and FL2. Impedance matchingresistors R6 and R7 are seen positioned within respective lines 344 and346. H-field winding 26 and its associated transformer 30 are configuredwithin an identical circuit as winding 28 and transformer 28. Thus, thatcircuit including preamplifier stage 36 is shown having the samecomponent identification as above but in primed fashion.

Now looking to the test coils 40 and 42, as well as the test coildrivers earlier described at 44, test coils 40 and 42 again areidentified in FIG. 11 by the same numeration. Test coil 40 is showncoupled via resistor R8 and lines 350 and 352 to +5 v supply asdeveloped by the voltage regulator earlier described at 50 and shown bythe same numeration in this figure. Similarly, coil 42 is seen coupledby resistor R9, line 350, and line 354 to -5 v supply as developed bythe regulator 50.

The opposite side of winding 40 is coupled to the collector of NPNtransistor Q1 while the corresponding opposite side of winding 42 isconnected to the collector of PNP transistor Q2. The collectors oftransistors Q1 and Q2 are commonly coupled by line 356. With thearrangement shown, when transistor Q1 is on, transistor Q2 is off and acurrent pulse flows through resistor R8 and winding 40 to generate amagnetic field. This field then is coupled into the antenna 24 for testor diagnostic purposes. Note that a diode D3 is coupled within line 358to the base of transistor Q1, while an oppositely oriented diode D4 iscoupled within line 360 to the base of transistor Q2. Lines 358 and 360,in turn, are seen to be coupled with singular line 46. Thus, where thesignal at line 46 is positive above ground, then transistor Q1 is turnedon on and transistor Q2 is turned off. Conversely, where the signal atline 42 is negative or below ground, then transistor Q2 is turned onthrough resistor R9 and transistor Q1 is turned off to effect thetransmission of a diagnostic or test pulse through winding 42.Accordingly, the positive signal drives the X channel and the negativesignal at line 42 drives the Y channel. Resistors R10 and R11 functionto maintain transistors Q1 and Q2 in an "off" state when there is notest pulse at line 42. Resistor R12 performs an attenuation functionwith resistor R13 to adjust the scale of the magnitude of the test pulseat line 46.

The mercury or gravity switch 54 again is represented in the drawingwith the same numeration as coupled between ground at line 362 and thetest line 46. The test signal is a.c. coupled to the test line 46, whilethis switch is d.c. coupled thereto. Note in this regard, the connectionof oppositely disposed line 364 through resistor R17 to +5 v at line 352and through resistor R16 to line 46. Thus, a d.c. term or level at testline 46 elevates up or down in conjunction with the position of switch54. Capacitor C6 within line 46 functions to block this d.c. signal.With the arrangement shown, the system can determine whether or not themercury switch 54 is connected. Thus, during an antenna test, if a d.c.term returns over the test line 46, the system will be aware that thegravity switch is performing.

The polarity sensing function within the sensor unit 10 again isrepresented to include a field plate shown as line 58. Line 58 is seencoupled by line 370 to one input of an operational amplifier 372. DiodeD6 and D7 perform a clamping function to dissipate transients or thelike and additionally are seen coupled through capacitor C10 to line 46.Capacitor C11 along with resistors R20-R22 provide an appropriateimpendance for the antenna 58 to drive. Amplifier 372 is the initialamplifier of three successive amplification stages including operationalamplifiers including additionally amplifier 374 and amplifier 376. Thesestages are configured with capacitors C12-C15 and resistors R23-R31 toprovide an amplified output at line 64. Resistor R32 and capacitor C16provide impedance matching with a coaxial cable which is represented bythe latter line 64.

The microprocessor and program memory function represented at block 132in FIG. 8 incorporates a variety of control routines and activitiesincluding a general handler activity for controlling program flow,responding to certain interrupts, and the like. Referring to FIG. 12,the functional association of the scheduler activity is presented inblock diagrammatic form. In the figure, the scheduler is represented atblock 380. As is apparent, the system performs actively in the presenceof a lightning strike. At such time, data become available and interactwith the scheduler program. This data-available association with thescheduler 380 is represented at block 382. The scheduler 380 alsoresponds to user functions as represented at block 384. These userfunctions are associated with the actuation of switches S1-S4 asdescribed in conjunction with FIG. 9. The time travel processrepresented at block 386 is an extension of the user function 384inasmuch as it is activated upon the pilot actuation of switch S1. Whenswitch S1 is so actuated, a determination is made as to whether data areavailable for this function to perform. If such data are available, thena flag is posted to cause the system to replay the data correspondingwith an assigned time lapse. In effect, the time travel process functionperiodically intervenes and controls where in data memory 200 thedisplay information comes from. Normally that information comes from themost currently filled part of memory. However, this particular function386 looks to the earlier-received and still-present information. Thefunction is quite valuable to the pilot inasmuch as it affords anopportunity to compare current data with past data to determine whetheror not a weather condition is worsening. A system diagnostic task asrepresented at block 388 primarily represents the activities surroundingthe generation of test pulses applied to the antennae for the purpose ofdiagnostics. The feature also includes a power-up testing of all memoryand other functions including the earlier-noted offset measurement andnulling procedure. A range zoom processor as represented at block 390also is triggered with the user function actuation of switches S2 or S3.For example, when a larger range is elected by the pilot, theilluminated pixels at the display will converge towards its center and,conversely, where a smaller range is elected by the pilot, theilluminated pixels will expand outwardly until the new range imaging iscompleted. The statistical modeler as represented at block 392 isrepresented as a collection of codes which function to assemble dataused to determine what the characteristics of the storm beingencountered are. Rather than providing a logic or forming decisionsbased upon a single stroke as has been the procedure of the past, theinstant program contemplates groups of strikes which may be consideredto represent the whole storm activity. Accumulated data then evolve astatistical model including strike rates in various quadrants utilizedfor analysis. Associated with the modeler activity 392 is an activityscanner function represented at block 394. This activity scannerfunction 394 identifies recent storm activity and calculates log to thebase 2 values for that activity. The logarithmic relationship isemployed, inasmuch as it provides a useful tool for activity data whichwill range from 0 to quite large values. By compressing these datalogarithmically a more effective evaluation procedure may be achieved.The display render function as represented at block 396 is a continuoussoftware task running between 3 and 5 Hz to update the data at thescreen or display. This updating must be sufficiently rapid or crisp toaccommodate, for example, heading changes of the aircraft where alldata, in effect, are rotated. Similarly, the earlier-described changesin range involve substantial display activities.

Referring to FIG. 13, the background signal test generator routine isdisplayed in flow diagrammatic fashion. The earlier-described testpulses must be uniquely identifiable from among all forms of interferingsources such as lightning or aircraft-based interfering sources, forexample, servo motors and the like. An initial consideration inachieving this uniqueness is the recognition that an external source ofinformation, for example from a lightning strike, will be transmittedthrough the atmosphere and will be received or picked-up by all of theantennas simultaneously. Similarly, where such an external source is sopositioned as to influence only one of the two H-field antennas, then nosignal will be received on one antenna while the entire signal will bereceived on the other. However, each of the coils 24 and 26 generallywill be influenced. However, the X-designated coil 24 is drivenseparately from the Y-designated channel or coil 26 under testconditions. Accordingly, the X-channel is driven or excited initiallyand about 15 microseconds later, the Y-channel is driven. Comparisonsthen are made based upon this sequential premise inasmuch as theopportunity for such a phenomenon to occur from an external source isquite remote. Therefore, the test pulses are analyzed for what is, ineffect, their unique signature. It may be noted that if the firstchannel to respond is the X-channel, then the two antennas are wiredcorrectly. However, if the first channel to respond is the Y-channel,then an indication that the antennas are wired backwards is present.Correction in software can then be made.

This program starts as a labelled "Background Signal Test Generator"routine as represented at block 400. The program then progresses to theactivity represented at block 402 calling for the generation of abipolar signal. This signal goes initially positive and then negative,the instruction at block 402 requiring that the initial pulse bepositive for one axis or the X-channel only. Then, as represented atblock 404, a delay of 15 microseconds is developed whereupon the bipolarsignal for the opposite axis or the Y-channel is developed. The testsignals of this test procedure are selected as being large enough totest the full dynamic range both of the amplification stages and theanalog-to-digital converters as at 154 and 158. Additionally, the slopeof the test signals are determined. This slope determination permits thesystem to evaluate the bandwidth of a given channel. In particular, theslew rate of the signal permits identification as to whether thebandwidths and phase are correct. It is important that the testprocedure have a high probability for detecting any error in the system.Thus, it is somewhat involved. Accordingly, the test inquires wellbeyond the presence or absence of a signal but to what form of signal isreceived. It may be observed that the acquisition of the test waveformdata is in the same manner as the acquisition of data emanating fromlightning strikes during non-test performance of the system.Verification also is made of gain and phase for each of the channels Xand Y. The resultant data are placed in memory for further evaluation.

The program then continues to decision block 408. The inquiry at block408 asks whether the test signal has been received in the X-channelfirst. If not, as represented at line 410 and block 412, the X- andY-channels are reversed and the program continues as represented atlines 414 and 416. In the event of an affirmative determination, theprogram continues as represented at line 416 to the inquiry representedat block 418. This inquiry determines whether the X-channel pulse ispositive first. If it is not, then the wiring into the X-channel isreversed and, as represented at line 420 and block 422, the X-channelpolarity is reversed in software. The program then continues asrepresented at lines 424 and 426. Where the X-pulse is positive first,then as represented by line 426 and block 428, a determination is madeas to whether the Y-pulse is positive first. In the event that it isnot, then as represented at line 430 and block 432, the Y polarity isreversed in software and the program continues as represented at lines434 and 436. Where the inquiry at block 428 is in the affirmative, thenthe program continues as represented at line 436. The inquiries atblocks 418 and 428 provide a set of decisions and related activitieswhich, in effect, rewire the instrument if necessary. A nextdetermination is developed in conjunction with block 438 wherein adetermination as to whether the polarity is correct. This is derivedthrough the imposition of a test signal upon the polarity sensor 48 asdeveloped through capacitor C10 and line 46 described in conjunctionwith FIG. 11. The polarity sensor is energized with one polarity duringone test occurrence and then is energized with the next polarity in anext subsequent test. In the event of an affirmative response, then asrepresented at line 440 and block 442, all remaining tests then areevaluated for correctness. These tests include bandwidth evaluation,gain evaluation, and phase evaluation which cannot be contemplated untilthe inquiries relating to proper configuration of the system are carriedout and corrections are made. In the general sequence of events with thetest procedure, a test pulse is scheduled by scheduler function 380 anda test pulse then is generated. The test pulse triggers the acquisitionsystem in the same manner as the response to a lighting strike. Theacquisition system then responds to the scheduler 380 to the effect thatdata are available. This information then is correlated with theinformation that a test is under way. An analysis then is made in theinstant test mode.

In the event that all tests are correct, then as represented at line 444and block 446, the test pulse phase is inverted for the next test to becarried out. This permits a test of both polarities of the polaritytesting plate of the sensor function 58. Note, that if the tests arecorrect, the phase is inverted. If the tests are not correct, the phaseis not inverted to provide further test control logic. Accommodation isadditionally made inasmuch as the test for polarity may coincide with alightning strike. Subsequent testing will effectively then re-evaluatethis function. If all testing shows the instrument to be in order, thenas represented at block 448, a test is scheduled to reoccur in oneminute. In the event of test failures, as represented at lines 450, 452,and block 454, the system continues to try the test and, in the event offailure, a predetermined number of times, for example, 8 times, then anerror signal is published at the display.

Turning to FIG. 14, an interrupt driven control feature is illustratedin block diagrammatic form. This interrupt, arbitrarily designated"Interrupt B" occurs where data are present and are to be acted upon.Thus, the start of this program is represented as a "Data AcquisitionControl". A first step in conjunction with such an interrupt commencedactivity is to save existing data and, as represented at block 462, theregisters and interrupt status of the control system are saved. Theprogram then progresses as represented at block 464. Instructionsrepresented with this block provide for the reading of strike polarity,which generally will have been developed in conjunction with the statusof a flip-flop component or the like. Then, as represented at block 466,the trigger point is read. The acquisition memory 178 is, in effect, acircular buffer responding to what is a continuously flowing stream ofdata from the analog-to-digital converters as at 154 and 158. It isnecessary to identify a data starting point or trigger. Thus, there isan association between the microprocessor function 132 and theacquisition hardware for developing a memory address. In effect, whenthe acquisition function stops and an address is read, 512 samples willhave occurred subsequent to a trigger. That data are read to memory,inasmuch as the acquisition hardware must be started again for a nextsequence. The program then continues to the activities represented atblock 468 wherein signal enhancement is commenced. This enhancementserves to increase the dynamic range and precision of the measurementsystem by carrying out calculations intended to identify or separatevalid data from noise. The goal at this juncture is to reach a pointwhere it is ascertained that the data are good or are invalid. Invaliddata are discarded quickly, such that as little investment as possibleis made in analyzing invalid data. The feature extraction component ofthis activity is one wherein certain special features of the incomingsignals are looked for, such as amplitude and waveshape. By testing withrespect to such features, 70% to 80% of erroneous data such as noisedeveloped from strobe devices, servo motors, and the like can bediscarded. As is apparent, the instrumentation must meet the challengeof dealing with a wide range of noise as well as valid signals. Theprogram then continues to the decision represented at block 470 whereina determination is made as to whether the waveform or data at hand hasthe attributes of a lightning strike or the attributes of signals notrepresenting a lightning strike. Such determination is made as a checkfor contamination. Where a determination is made that lightning strikederived data are at hand, then as represented at line 472 and block 474,an activity ensues which provides for the completion of signalenhancement and the transfer of data to data memory. As long as thatwaveform is in acquisition memory 178, the acquisition system cannot bereactivated to receive more data without losing the data now at hand.Thus, the transfer is made and the acquisition memory is released. Thesedata will have a very high probability of being valid. Time is now takento complete signal enhancement in conjunction with the data now placedin data memory. The program then continues to block 476 whereinactivities for the management of signal buffers are carried out. Forexample, the system will buffer numerous lightning strikes. In thisregard, if the system is calculating data with respect to a givenlightning strike and a next strike occurs, the data corresponding withthat next strike are saved and the system then returns to carry on theoriginal calculations. A sequence of lightning strikes all will becaptured and processing will be postponed. Thus, antenna activity isdesignated as having a higher priority than calculations made withrespect to previous data. Generally, lightning strike evolved data willoccur in clusters followed by intervals of silence. In effect, the peakdata rate evidenced with lightning strike clusters will be higher thanthe calculating speed of the computational systems, however, that systemwill accommodate an average of that rate of data acquisition. Bufferingaccommodates for this situation. Generally, data representing about sixstrikes may be buffered with this feature. Typically two or threebufferings are carried out in the operation of the system. Inconventional manner, flags are posted for further background signalprocessing following the acquisition procedure.

At this point in time, the acquisition memory will have been freed ormade available, data having been copied elsewhere and, as represented atblock 478, the acquisition system is restarted, the registers andinterrupt status being restored. The interrupt then is exited asrepresented at block 480. Where the determination at decision block 470is in the affirmative that contamination is present, then as representedby line 482 and block 478, the acquisition system is restarted andregisters and interrupt status are restored.

Referring to FIG. 15, the background signal processing features of thecontrol system are described in flow diagrammatic fashion. In general, adetermination will have been made by the system at this point as towhether a test is under way, or as to whether the data acquired emanatesfrom a lightning strike. The present control features are concerned withthe latter condition. Entry into the activity is represented at block490 and will have been ultimately commenced or triggered by anacquisition interrupt evidenced by the posting of a flag for furtherbackground signal processing as discussed in connection with block 476of FIG. 14. The latter flag is checked by the scheduler 380 whichdetermines that background signal processing should be carried out. Atthis point in time, data are present in data memory 200 which will be aprocessed waveform from both the X and Y channels. As represented atblock 492, a Fourier transform is carried out and various features arelooked for as developed from this transform activity. Generally, theFourier transform (FFT) will provide frequency information with respectto amplitude as well as phase information. A variety of FFT orequivalent techniques may be employed for this purpose. Certaincharacteristics will permit an identification as to the form of strikeunder evaluation. In particular, it may be determined as to whether thedata represents a leader or a return stroke. The leader phenomenon is aform of a primer exhibiting a very brief duration, low amplitude signalionization path. Termed a "dart" leader, it will occur prior to a fulllightning strike. Very often, the dart leader occurs from cloud toground and serves as the initial ionization path for conduction tooccur, for example from ground to cloud. Generally, the dart leader willexhibit a higher percentage of higher frequencies. By contrast, thereturn stroke contains a greater quantity of lower frequencies andtypically will exhibit a much higher in amplitude. Accordingly,activities which ensue following categorization may be represented byline 494 and block 496 wherein a dart leader is identified and theactivity continues as represented by lines 498 and 500. On the otherhand, the categorization may be that of a return stroke as representedby line 502 and block 504. Line 500 is seen to lead to the activitiesrepresented at block 506 which include the calculation of the bearing ofthe strike which is based upon the magnitude of the signals invoked incoils 24 and 46. Polarity correction is provided in conjunction with theinformation from the polarity sensor 48 and top/bottom correction ismade with respect to the orientation of the sensor unit 10 inconjunction with the output of the gravity or mercury switch 54. Thepolarity correction provides for a 180° adjustment to the computations.

The activities then continue as represented at block 508 wherein arelative range value is calculated. This value is a number used later todevelop a more precise range which ultimately is displayed. It, ineffect, represents a first derived value for that parameter. Thisrelative range then is stored as well as the bearing of the strike, theaircraft heading and the time of strike occurrence. Time data aredeveloped in conjunction with the commencement of activity or start-upof the system and provide information as to how far back in time, forexample, strike data will have occurred for utilization and evaluationof the earlier-noted time travel feature. Additionally, data at thedisplay is caused to disappear after a certain period of time, inasmuchas it will no longer be useful. Generally, this timing is to an accuracyof about 1000th of a second. The activities then progress as representedat block 510 to carry out linking of the data structure. This, ineffect, is a data tracking activity wherein, for every strike, the datastored in memory are so stored with appropriate pointers, linking,indexing and the like. The "Update active table" function is is onewherein the storm characteristics at various places or locations in thesky are monitored. This monitoring is carried out in a table update formof processing activity. At this juncture, the lightning strike will havebeen analyzed, buffered, and the data represented by it appropriatelytreated and linked into the data memory structure. The buffer area is nolonger required for the instant data and thus, is released for responseto the next lightning strike occurring. As represented at block 512, areturn is made to the scheduler 380.

Returning to block 492, the categorization of the strike may, asrepresented at line 514 and block 516, indicate that coincidentcontamination is at hand. With that categorization, as represented atline 518, the activity exits to return to the scheduler 380. In general,coincident contamination is a phenomenon wherein two lightning strikesoccur simultaneously in different parts of the same storm. Unless it isdealt with as shown, in view of the 80 microsecond window of evaluation,in effect, a blizzard of pixels will occur at the display having novalue to the aircraft pilot.

Looking to FIG. 16, activities representing the development of headinginformation from, for example, a rotary transformer form of compass isdescribed. In particular, at block 530, this activity is entered withrespect to the earlier-described "synchro" heading developed from somecompass systems. Generally two 400 Hz outputs are evolved, theamplitudes of which varies upon the angle which the device is orientedto. As represented at block 532, the X-and Y-synchro outputs are read,digitized, and average over 8 samples for the purpose of removing noise.As represented at block 534, the data are converted from eliptical torectangular coordinates inasmuch as the data as acquired will be basedupon a 120° aspect and the conversion provides the data with respect toa 90° reference. The heading then becomes the arctangent of the X and Ycoordinate signals. As represented at block 536, the activity then exitsto the scheduler management. Other heading sources may be stepper motorderived in response to gyro-originated heading data and the like.Another heading source may be derived from typical Loran track outputs.This can be inserted into the system through an RS 232 connection. Theupdate rate from the systems is generally adequate to provide usefuldata.

The display or readout is updated at a 76 Hz rate. This update activityoccurs in conjunction with an interrupt designated "interrupt A" asrepresented at block 550 in FIG. 17. Looking to that figure, theinterrupt activity commences with the saving of registers andpre-interrupt status of the system as represented at block 552. Theactivity then progresses as represented at block 554 to reset thedisplay control and, select a display frame. In general, the displaymemory 218 will be formed of two groups of two pages of the frames and apixel selection may be positioned on one or both of such pages.Different intensities of the pixel output or the modulation thereof maybe developed by locating this pixel on one or both of the pages offrames. In general, one such memory frame is being updated while thedata of the other is being displayed. The reset feature described in theblock is representative of the commencement of update. In general,display intensity is based upon the interval at which a given pixel isenergized. Selection of intensity is based upon the cabin ambientillumination intensity as monitored by photocell 307 described inconjunction with FIG. 10. The activity then continues, as represented bydecision block 556 wherein a determination is made as to whether asubstantial heading change is under way. In the event that it is, thenas represented at line 558 and block 560, the current heading is updatedand bank angle and turn rate are computed. Thus, distortion resultingfrom the turning activity of the aircraft is corrected. The program thencontinues as represented at lines 562 and 564. Where no heading changeis at hand, then the program also continues as represented at line 564to the inquiry at block 566. Here, the general system timer isincremented and a check is made as to whether an overflow condition isat hand with respect to it. In the event of an affirmative determinationat block 566, then as represented by line 568 and block 570, the mostsignificant byte is incremented and the program continues as representedat lines 572 and 574. Line 574 also indicates no overflow condition isat hand, and leads to the activity represented at block 576. Thisactivity involves the sampling of switches S1-S4 and identifying apositive transition of them. The latter transition is the only one actedupon by the system. Accordingly, as represented by decision block 578,where a positive transition, representing a button push, is present,then as represented by line 580 and block 582, background flag bits areset in accordance with the switch actuated, thus providing appropriateinformation as to that fact to the scheduler 380. The program thencontinues as represented at lines 584 and 586. Block 588 describes thatthe ambient light is measured by the photocell 307 and display intensityis updated. This update activity occurs each half second. Theapplication of a rate limit provides that the update occurs only by onebrightness step. This accommodates for transient interruptions of thelight input to the photocell as may occur by the movement of a handorthe like in the aircraft cabin or the like. The interrupt program thenexits with the restoration of the register sets as represented at block560.

Since certain changes may be made in the above system, method andapparatus without departing from the scope of the invention hereininvolved, it is intended that all matter contained in the abovedescription or shown in the accompanying drawings shall be interpretedas illustrative and not in a limiting sense.

I claim:
 1. Storm monitoring apparatus mountable with respect to aheading axis, for locating lightning occurrences evoking anelectromagnetic field including a magnetic, H-field component and anelectrostatic, E-field component, comprising:a first H-field antennaincluding a first coil structure having a first array of windingsoriented at a select angle with respect to said heading axis andderiving a first current response to said H-field component; a secondH-field antenna, including a second coil structure having a second arrayof windings orthogonally disposed with respect to said first array andderiving a second current response to said H-field component; a firsttest winding positioned in adjacency with said first coil structure andexcitable to impose a first test magnetic field thereupon to effectgeneration of a first test current response therein; a second testwinding positioned in adjacency with said second coil structure andexcitable to impose a second test magnetic field thereupon to effectgeneration of a second test current response therein; control meansresponsive to said first and second current responses for derivinglightning occurrence, bearing and range information outputs, forintermittently exciting said first and second test windings, forcomparing each said first and second test current responses with apredetermined value of current response, and for deriving an erroroutput when said comparison represents an improper response performance;and a perceptible readout responsive to said information outputs forpublishing said occurrence, bearing and range information, andresponsive to said error output for providing a perceptible indicationthereof.
 2. The storm monitoring apparatus of claim 1 including:a drivernetwork responsive to a first test signal of first polarity to effectsaid excitation of said first test winding, and responsive to a secondtest signal of second polarity to effect said excitation of said secondtest winding; and said control means derives said first and second testsignals for assertion along an electrical path to said driver network.3. The storm monitoring apparatus of claim 2 in which said electricalpath includes a single electrical lead extending from said control meansto said driver network for carrying said first and second test signals.4. The storm monitoring apparatus of claim 1 including:agravity-actuated switch coupled with a d.c. power source mounted withsaid first and second H-field antennas and conveying a predeterminedd.c. signal level to said electrical path only when in a normalorientation; and said control means is responsive in the absence of saidd.c. level to derive an error signal.
 5. The storm monitoring apparatusof claim 1 in which:said first and second arrays of windings includeprinted conductive strips upon printed circuit supportive substrates;and said first and second test windings include printed conductive teststrips formed upon said printed circuit supportive substrates adjacentsaid strips of said first and second arrays of windings.